U.S. Pat. Nos. 5,616,418 and 5,506,310 disclose a structure consisting in succession of a polyamide layer, a layer made of a polyamide elastomer/grafted polyolefin blend and a layer that may be made of wood from a metal, epoxy or polyurethane. This structure may be a ski, that is to say the epoxy or polyurethane layer is not a thermoplastic layer but is the core of the ski. This part of the ski is not thermoplastic—the epoxy resin is crosslinked even if it is a polyurethane, i.e. a rigid polyurethane.